Wissen für Morgen

Knowledge for Tomorrow

Institut für Technische Thermodynamik

Zinc-air batteries have the high energy density of metal-air batteries combined with the features of zinc, which are the safe and easy handling, the environmental acceptability and the abundance of zinc. The only limiting factor for the capacity is the amount of reversible active usable zinc inside the battery. This is due to the high passivation rate and dendritic growth of zinc. Another limiting factor is the high overpotential during charge and discharge and corrosion of cathode materials. In this work an Ag/Co3O4 electrode was used and stable performance over 170 cycles in a full cell were achieved. This electrode was investigated under various conditions to improve the performance and cycle life.

Production and characterization of bi-functional cathodes for secondary zinc-air batteries A. Kube, D. Wittmaier, N. Wagner, K. A. Friedrich German Aerospace Center, Institute of Engineering Thermodynamics Pfaffenwaldring 38-40, 70596 Stuttgart Corresponding author: alexander.kube@dlr.de

• Ag/Co3O4 electrode measured in 7.5 M KOH at RT with a O2 pressure of 3 mbar

• Increase of pressure leads to electrochemical performance loss

• Impedance spectra shows increase in diffusion impedance

• Inductive loop for small frequencies shows electrochemical activity of backing GDL → electrode is completely flooded above 11.5 mbar

• Over 170 cycles were achieved for

KOH based systems

• Potential window for 2.5 cm² and 25 cm² cell are in good agreement

• Co3O4 particles cover the surface of Ag

particles almost completely, as shown in the EDX measurement on the left

• XRD-measurement shows presence of AgIAgIIIO2 and Ag2

IO at 1.8 V vs. RHE. For longer dwell times at 1.8 V, the Ag2

IO will also be transformed to AgIAgIIIO2

• XRD-measurements at 0.3 V vs. RHE show

the presence of metallic Ag

H.M.A. Hatem, H. Baltruschat, D. Wittmaier, K.A. Friedrich, Electrochimica Acta 151 (2015) 332–339

Conductive additive + catalyst + PTFE Mixing Hydraulic pressing Gas diffusion electrode (GDE)

This work is supported by the European Commission – Grant Agreement 646186 - ZAS

Ag

Co3O4

30 cm

10

cm

• A stable and active catalyst combination for Zn-air batteries was developed and over 170 cycles in a full

cell Zinc-air battery was shown • Only around 11.5 mbar are needed to flood the electrode • The change of oxidation states from pristine Ag to Ag2

IO and AgIAgIIIO2 and back to pure metallic silver were measured with XRD

25 cm² cell // 7.5 M KOH 2.5 cm² cell // 7.5 M KOH

2.5 cm² cell // 1 M LiOH

Introduction

Production Technique

Surface characterization

Conclusion

Full Cell Testing/Scalability Hydrostatic Pressure